In a mortar, gently pound the rosemary leaves with the 1/4 cup of olive oil to flavour the oil. Transfer the oil to a large bowl. Add the marrow bones and toss to coat. Season the bones with salt and pepper, cover with plastic wrap and refrigerate overnight.

Preheat oven to 180C (390F)

Wrap the marrow bones in foil in 2 packets and add bacon pieces to each and arrange them on a large tray and cook in the oven for 30 minutes. Open the foil packets, stand the bones on their ends on the tray and continue to cook for an additional 15 minutes until the marrow is warmed throughout and starting to sizzle.

Carefully remove the bones from the oven and let them cool down. When cool enough extract the marrow to the bowl of a food processor.

Melt 100g (4 oz) or half of the butter in a pan over a medium heat, then add the onion and fry until softened, but not coloured.

Add the garlic, bay leaf, thyme and chicken livers and fry the livers until golden-brown all over and cooked through, season well with salt and freshly ground black pepper.

Add the Madeira to the pan and boil until reduced to a couple of tablespoons. Remove the bay leaf and place the liver mixture and 5og (2 oz) of the remaining butter into a food processor along with the bacon and bone marrow. Blend until smooth. Season, to taste, with salt and freshly ground black pepper and give it another pulse to combine.

Place the puree into six 100g (4-oz) ramekins or 1 serving terrine and smooth the top. Melt the remaining butter and pour on top of each ramekin or serving terrine, then refrigerate until set. Approximately 30 to 40 minutes.